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I'm testing the performances of my new SSD card, and it seems I'm stuck with sata2 speed even if my controller is sata3.

Here is the command I'm using.

dd if=tempfile of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1,1 GB) copied, 0,309558 s, 3,5 GB/s

I got 3,5GB/s even if my device is SATA3:

dmesg | grep SATA

[    7.035956] ahci 0000:00:1f.2: AHCI 0001.0300 32 slots 6 ports 6 Gbps 0x5 impl SATA mode
[    7.051861] ata1: SATA max UDMA/133 abar m2048@0xf7a16000 port 0xf7a16100 irq 43
[    7.051866] ata3: SATA max UDMA/133 abar m2048@0xf7a16000 port 0xf7a16200 irq 43
[    7.368593] ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[    7.368621] ata3: SATA link up 1.5 Gbps (SStatus 113 SControl 300)

hdparm -iI /dev/sda | grep SATA

Transport:          Serial, ATA8-AST, SATA 1.0a, SATA II Extensions, SATA Rev 2.5, SATA Rev 2.6, SATA Rev 3.0

Here is my controller:

lspci | grep SATA

00:1f.2 SATA controller: Intel Corporation 7 Series Chipset Family 6-port SATA Controller [AHCI mode] (rev 04)

This is the hdparam test:

 hdparm -I /dev/sda | grep -i speed
           *    Gen1 signaling speed (1.5Gb/s)
           *    Gen2 signaling speed (3.0Gb/s)
           *    Gen3 signaling speed (6.0Gb/s)

Partition alignment should be ok (I'm not 100% sure).

(parted) p                                                                
Model: ATA Samsung SSD 840 (scsi)
Disk /dev/sda: 250GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system     Flags
 1      1049kB  92,9GB  92,9GB  primary  ext4
 4      92,9GB  94,0GB  1128MB  primary  ext4            boot
 2      94,0GB  241GB   147GB   primary  ext4
 3      241GB   250GB   9222MB  primary  linux-swap(v1)

(parted) align-check opt 1                                                
1 aligned
(parted) align-check opt 2
2 aligned
(parted) align-check opt 3
3 aligned
(parted) align-check opt 4
4 aligned

Bios is configured correctly with AHCI

My laptop is an Asus A55VD, SSD is Samsung EVO 840.

Why I'm having 3GB/s instead of 6GB/s?

Is perhaps my disk alignment not correct?

Thanks

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3.5 GB/s is actually 28 Gbps (not taking protocol overheads into account) as GB/s is GigaByte/s, it is actually quite impossible to get that high speed over that interface.

Some relevant observations: * Your test is far too short to really evaluate speed, increase the read buffer size to see it averaged better. * It is rather likely that the data "read" was already in the cache, I recommend adding "direct" to the command line to prevent that.

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